Visualize the 7-layer OSI model and 4-layer TCP/IP model. Watch data encapsulation as it travels down the sender stack, across the network, and up the receiver stack.
Data starts at the Application layer. Each layer adds its own header (and sometimes trailer) as it moves down the stack. By the Physical layer, the original data is wrapped in all protocol headers.
The fully encapsulated packet (now a frame at Layer 2, then bits at Layer 1) travels across the physical medium -- copper wire, fiber optic cable, or wireless signals.
At the receiver, each layer strips its corresponding header as data moves up the stack. The Application layer receives the original data, now fully unpacked.
| Layer | Name | PDU | TCP/IP | Responsibility |
|---|---|---|---|---|
| 7 | Application | Data | Application | Provides network services directly to end-user applications |
| 6 | Presentation | Data | Application | Translates data between application and network formats |
| 5 | Session | Data | Application | Establishes, manages, and terminates sessions |
| 4 | Transport | Segment | Transport | Provides reliable or unreliable end-to-end data delivery |
| 3 | Network | Packet | Internet | Routes packets from source to destination across networks |
| 2 | Data Link | Frame | Network Access | Transfers frames between adjacent network nodes |
| 1 | Physical | Bits | Network Access | Transmits raw bitstreams over a physical channel |